In opera, she is foolhardy (4)
I believe the answer is:
rash
'foolhardy' is the definition.
('rash' can be a synonym of 'foolhardy')
'in opera she is' is the wordplay.
'in' says the answer is hidden in the clue.
'RASH' can be found hidden inside 'opera she is'.
(Other definitions for rash that I've seen before include "Flood" , "Foolhardy about the skin infection" , "Headstrong" , "Ill-advised" , "Impulsive - eruption" .)